New York’s Guggenheim Museum said it will not include three works in an upcoming exhibition after they sparked the ire of animal rights groups. The exhibition, “Art and China after 1989: Theater of the World,” included three works that critics said promoted cruelty to animals–including one called “Dogs That Cannot Touch Each Other,” which reportedly included footage of pit bulls on treadmills.

The museum initially defended showing the works, saying it valued freedom of expression, but it said in a statement yesterday that threats of violence have forced it to reconsider out of concern for the safety of its visitors. It added that it is “dismayed” over having to basically self-censor its exhibition:

“Out of concern for the safety of its staff, visitors, and participating artists, the Solomon R. Guggenheim Museum has decided against showing the art works Dogs That Cannot Touch Each Other (2003), Theater of the World (1993), and A Case Study of Transference (1994) in its upcoming exhibition Art and China after 1989: Theater of the World. Although these works have been exhibited in museums in Asia, Europe, and the United States, the Guggenheim regrets that explicit and repeated threats of violence have made our decision necessary. As an arts institution committed to presenting a multiplicity of voices, we are dismayed that we must withhold works of art. Freedom of expression has always been and will remain a paramount value of the Guggenheim.”

An online petition denouncing the museum attracted more than 600,000 supporters as of today. You can learn more about the controversial works here. But as of now, you can’t actually see them at the Guggenheim.